1. Field of the Invention
The present invention generally relates to an apparatus and method for separating integrated circuit structures connected by interconnects such as ball grid arrays and column grid arrays.
2. Description of the Related Art
Ball Grid Arrays (BGA) and Column Grid Arrays (CGA) are widely used to electrically and mechanically connect substrates (typically ceramic) carrying semiconductor chips to a card. The BGA commonly consists of an array of metal balls which are soldered to a substrate by means of a solder fillet material. The solder fillet material is typically of a lower melting temperature (183 C for eutectic Pb/Sn) than the solder ball (˜280 to 300 C) which it is joining to, enabling the solder ball not to melt during joining. However, the solder ball and fillet material may be of the same composition, thus causing the entire interconnect to reach liquidous temperature during the reflow. During the manufacturing process, a substrate, either organic or ceramic, is attached to a carrier. Typically, this carrier is organic and may be comprised of FR4 like material, or may have Surface Laminar Circuitry (SLC) on a core made of other organic material. If the substrate requires rework, such as because of a defective chip, the substrate must first be removed from the carrier.
One conventional method to remove a substrate from a card uses hot gas. In such a method, a gas, typically nitrogen, is heated to high temperatures and impinged upon the substrate. The tooling for such an operation is dedicated. Further, such an operation is typically performed in batch mode. There are numerous problems with employing such a method when removing a ceramic substrate from an organic carrier. First, hot gas uses a significantly greater amount of thermal energy that is transmitted to the top surface of the substrate. Such high temperatures can damage the still good chips atop the substrate, or make failure analysis for the defective chips not possible. The former situation may arise when the substrate has two or more chips, with one being defective, and the others being good. More importantly, such methods cannot be used for higher liquidous temperature alloys, such as those being developed for lead free applications, because the higher amount of heat input would damage organic boards which typically cannot exceed temperatures greater than 250 C. As an example, a lead-free alloy comprising Sn, Ag and Cu (95.5 wt % Sn, 3.8 wt % Ag and 0.7 wt % Cu) has a liquidous temperature equal to approximately 217 C. The hot gas technique can cause excessively high temperatures at the organic board or carrier surface, when it attempts to melt this lead-free alloy which resides between the ceramic substrate and organic board. Thus, a need exists to separate the substrate from the carrier while preserving its ability to be rejoined to another carrier.